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Successful parasitism relies on the evasion of adversarial host responses. Wang et al. have recently shown that Toxoplasma gondii relies on the protein phosphatase 2A (PP2A) to cause persisting infections. The phosphatase controls the development of dormant parasite stages and the accumulation of sugar supplies. [ABSTRACT FROM AUTHOR]

Abstract: Apicomplexan parasites undergo metabolic shifts in adaptation to environmental changes. Here, we investigate the metabolic requirements which are responsible for ATP homeostasis in the extracellular stage of Toxoplasma gondii. Surprisingly, we found that freshly released tachyzoites are able to maintain a constant ATP level during the first hour of extracellular incubation without the acquisition of external carbon sources. We further demonstrated that the extent of gliding motility and that of host cell invasion is independent from the availability of external carbon sources during this one hour extracellular period. The ATP level and the invasion efficiency of extracellular parasites were severely decreased by treatment with the glycolysis inhibitor, 2-deoxy-d-glucose, but not by the F0F1-ATPase inhibitor, oligomycin. This suggests that although the uptake of glucose itself is not required during the 1h incubation period, extracellular parasites depend on the activity of the glycolytic pathway for ATP homeostasis. Furthermore, active glycolysis was evident by the secretion of lactate into the culture medium, even in the absence of external carbon sources. Together, our studies suggest that tachyzoites are independent from external carbon sources within the first hour of their extracellular life, which is the most relevant time span for finding a new host cell, but rely on the glycolytic metabolisation of internal carbon sources for ATP maintenance, gliding motility and host cell invasion. [Copyright &y& Elsevier]

The fuel property effect on a high-pressure ballistic injection cycle is studied by n -dodecane and n -heptane because these pure fuels have well-known and well-specified properties. Distinct differences between both fuels are worked out for a ballistic injection cycle by dynamic 3D flow simulations. A two-phase volume of fluid Euler–Euler method for gas mixture is utilized to capture both cavitation and primary breakup in a seamless simulation of injector internal flow and near-nozzle spray. The split-off of primary ligaments is directly resolved down to the available grid limit in computational grid with about 100 million cells. A large-eddy simulation is employed. The simulation results are complemented by laser-induced fluorescence measurements of the spray's near field. The spray head exhibits a mushroom shape for n -dodecane during the early opening phase, while a more complex and unstable misty initial spray head, which is attributed to lower density and viscosity, is observed for n -heptane. For high needle lift, the intensity of string cavitation is lower for n -dodecane due to its larger density and viscosity. During the opening phase, highly unsteady turbulent vortex and cavitation structures are generated. For n -dodecane, these structures survive far into the closing phase. This behavior is attributed to an inertia effect due to the larger density. This hysteresis is also observed for the ligament velocity, which still increases during the early closing phase. For n -heptane, the hysteresis is much less pronounced and ligament velocities are higher due to the lower density. • Cavitation and primary breakup are treated simultaneously in a seamless simulation. • Effect of in-nozzle flow on subsequent flow physics is illustrated. • Shape of spray head is density- and viscosity-dependent. • Different structures occur in opening and closing phase (fuel-dependent hysteresis). • High fuel density promotes survival of structures from opening into closing phase. [ABSTRACT FROM AUTHOR]

Apicomplexan parasites, such as Toxoplasma gondii, are unusual in that each cell contains a single apicoplast, a plastid-like organelle that compartmentalizes enzymes involved in the essential 2C-methyl-D-erythritol 4-phosphate pathway of isoprenoid biosynthesis. The last two enzymatic steps in this organellar pathway require electrons from a redox carrier. However, the small iron-sulfur cluster-containing protein ferredoxin, a likely candidate for this function, has not been investigated in this context. We show here that inducible knockdown of T. gondii ferredoxin results in progressive inhibition of growth and eventual parasite death. Surprisingly, this phenotype is not accompanied by ultrastructural changes in the apicoplast or overall cell morphology. The knockdown of ferredoxin was instead associated with a dramatic decrease in cellular levels of the last two metabolites in isoprenoid biosynthesis, 1-hydroxy-2-methyl-2-(E)- butenyl-4-pyrophosphate, and isomeric dimethylallyl pyrophosphate/isopentenyl pyrophosphate. Ferredoxin depletion was also observed to impair gliding motility, consistent with isoprenoid metabolites being important for dolichol biosynthesis, protein prenylation, and modification of other proteins involved in motility. Significantly, pharmacological inhibition of isoprenoid synthesis of the host cell exacerbated the impact of ferredoxin depletion on parasite replication, suggesting that the slow onset of parasite death after ferredoxin depletion is because of isoprenoid scavenging from the host cell and leading to partial compensation of the depleted parasite metabolites upon ferredoxin knockdown. Overall, these findings show that ferredoxin has an essential physiological function as an electron donor for the 2C-methyl-D-erythritol 4-phosphate pathway and is a potential drug target for apicomplexan parasites. [ABSTRACT FROM AUTHOR]